Use hex checsum for hash key instead of raw (issue1723043)

[zhoresh]

Reviewers: dev-remailer_shindig.apache.org, johnfargo,
Description:
To make it easy to debug and support, changing cache keys to use hex
checksum instead of raw checksum

Please review this at http://codereview.appspot.com/1723043/show

Affected files:
  java/common/src/main/java/org/apache/shindig/common/util/HashUtil.java
   
java/gadgets/src/main/java/org/apache/shindig/gadgets/parse/GadgetHtmlParser.java
   
java/gadgets/src/main/java/org/apache/shindig/gadgets/parse/caja/CajaCssLexerParser.java
   
java/gadgets/src/main/java/org/apache/shindig/gadgets/parse/caja/CajaCssParser.java
   
java/gadgets/src/main/java/org/apache/shindig/gadgets/servlet/CajaContentRewriter.java
   
java/gadgets/src/main/java/org/apache/shindig/gadgets/templates/TemplateLibraryFactory.java